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Hypersonic Shock Tunnel
Hypersonic shock tunnel is essentially short duration hypersonic wind tunnel used for testing the hypersonic vehicles configuration like launch vehicles, missiles and space shuttles flying at Mach number higher than 5. Schematic diagram of a typical hypersonic shock tunnel is shown in the accompanying diagram. It consists of a shock tube connected to a convergent divergent hypersonic nozzle which is in turn connected to a test section and a dump tank. Driver and driven sections of shock tube are separated by a metallic diaphragm while the nozzle and the shock tube are separated by a thin paper diaphragm. Test model is mounted in the test section which is evacuated to very high vacuum initially using vacuum pump. Operation of the hypersonic shock tunnel is very complex and the facility is more suitable to carry out research work and hence it is seldom used for teaching purpose at undergraduate level.
Applications of Shock Tunnel
The hand driven hypersonic shock tunnel is capable of generating Mach 6 flow in the test section for a very short time of the order of 150 200 s. Using instrumentation that works at a faster rate, aerodynamic measurements may be made. Below are listed some of the basic experiments that can be performed.
As stated above the conventional hypersonic shock tunnel is more a research facility and facility for producing the design data for practical flight vehicles. But teaching of hypersonic aerodynamics at undergraduate and postgraduate levels is incomplete unless students are allowed to conduct practical experiments in the laboratories. For this purpose, Prof. K. P. J. Reddy invented hand operated table top hypersonic shock tunnel named Reddy Tunnel which is ideally designed for conducting practical classes in colleges offering Aerospace Engineering degree courses. In addition, this facility can be used by all branches of engineering degree for carrying out project works. More importantly PhD and Post Graduate students of all branches can use this facility to undertake their thesis work. Advise on carrying out research using Reddy Tunnel can be obtained from SESPL.
Technical Specifications Shock Tube: Wind Tunnel Section:
Diameter : 29 mm
Driver tube length : 400mm
Driven tube length : 600mm
Diaphragm material : paper
Hypersonic Nozzle : Convergent divergent nozzle of 80 mm exit diameter.
Test section : Rectangular test section with optical windows.
Dump tank : Cylindrical dump tank with model mounting base and facility for data throughput.
Diaphragm rupture pressure monitor.
High speed pressure sensors for measurement of
Shock speed
Pressures behind primary shock wave
Pressure behind reflected shock wave
Data acquisition oscilloscope.
Vacuum pump to create vacuum in test section and dump tank.
Working Parameters
Maximum model dimension: 50 mm (crosswise)
Flow Mach number: 6
Maximum effective test time: 300 µs
Test gas: Typically air but can be changed as required.
List of experiments:
Calibration of core flow : Due to boundary layer effect in the free stream, the outer part of the flow will be slower and have different flow parameters compared to the inner core. It is essential to locate the extent of the core using pressure measurements so that the test model can be designed to be smaller than that dimension.

Measurement of drag and lift co-efficient : Single point or three point accelerometers may be used to measure the drag of aerodynamic shapes so as to figure out methods to reduce it.

Measurement of surface pressures : Fast acting pressure sensors are generally procured from PCB Electronic and Kulite Semiconductors. These can measure pressures as high at 100 bar within a time of less than 5 µs intervals. The sensors are generally expensive, but quite accurate and robust. A few of these sensors may be used to map the surface pressure experienced by common aerodynamic shapes. Moreover, because of the fast acquiring rate, flow fluctuations can also be studied.

Measurement of heat fluxes : Heat flux measurement may be done using thin-film sensors or thermocouples. These also work with a similar speed of the pressure sensors. IISc lab has vast experience in fabricating and using platinum and nickel thin-film sensors, and is just starting to try fast acting thermocouples.

Measurement of pitching and yawing moments : Accelerometers mounted in lateral orientation to the flow can be employed to measure the forces of pitching and yawing experienced by aircraft models, especially non-axisymmetric ones, or models at an angle of attack.

Schlieren flow visualization studies :
Using a special flow visualization technique that involves plane and concave mirrors, the shock waves around bodies in the free stream flow can be observed. This gives good insight into the flow structures and so on.
Customizations Available
Gas driven tabletop hypersonic shock tunnel
The gas driven shock tube can be incorporated into a shock tunnel thereby increasing the maximum flow stagnation enthalpy to up to 3 MJ/kg.
Full scale hypersonic shock tunnel
This instrument will measure in excess of 10 m. The test section area can be increased to suit any size of test model. Flow stagnation enthalpy of up to 5 MJ/kg can be achieved.